WO2001052604A1

WO2001052604A1 - Microwave system with at least two magnetrons and method for controlling said system

Info

Publication number: WO2001052604A1
Application number: PCT/IB2000/000025
Authority: WO
Inventors: Georges Roussy
Original assignee: R.I.M.M. Technologies N.V.
Priority date: 2000-01-10
Filing date: 2000-01-10
Publication date: 2001-07-19
Also published as: CA2397137C; JP4426149B2; AU2000217929A1; JP2003519894A; CA2397137A1

Abstract

Disclosed is a heating system or microwave processing system for a material or an object, comprising an applicator or oven (5) which is fed by two separate magnetrons (11, 12). The magnetrons are mounted on the combined branches (3, 4) of a magic T-coupler or directional coupler, forming a ring. The other combined branches (1, 2) irradiate the material (10). Impedance adapters (8,9) are disposed in the branches (3,4) and/or in front of the magnetrons (11, 12) for decoupling the operation of the magnetrons and transmission of the full amount of power emitted by the magnetrons to the material or object. According to the method described, it is possible to obtain a constant, homogeneous, maximum distribution on the object or material, or inversely, a distribution which is modulated according to the material or object, i.e. a maximum amount of central distribution and less distribution on the surface, by adjusting the impedance adapters with the aid of dual balanced mixers, for example.

Description

MICROWAVE INSTALLATION WITH AT LEAST TWO MAGNETRONS AND METHOD FOR MONITORING SUCH AN INSTALLATION

Making a microwave applicator to heat a given product, having a given geometry, is always a case in point. Although many solutions have been proposed, none is general enough to solve all of the engineer's problems. The multimode cavity, which is the basis of the construction of domestic ovens, works optimally for products whose volume is close to 1 dm ³ . For smaller or larger volume products, the oven performance is poor. The heating time must then be increased prohibitively for many semi-industrial applications.

Let's compare, for example, the case of reheating a bun containing a slice of meat or cheese that comes out of the freezer where it was stored at -18 ° C. To bring the temperature down to 35 °, with a domestic microwave oven, with a nominal power of 800 W, it is necessary to heat five minutes.

Suppose that we know how to guide the radiation emitted by a generator in a guide of the same dimension as the object, the penetration of waves in the product is close to 2 cm. This means that if we neglect the reflection of the waves on the input face of the object, or if we adapt the received power by having before it a suitable impedance adapter, the object will be traversed by a wave whose l attenuation will be half every 4 cm. Given the thickness of the object, one third of the incident power will exit the object from the opposite side. Although it is possible to reflect this power towards the object, the entry face will always be better heated than the opposite face. The product may eventually burn on the inlet side, before it is hot on the opposite side.

In EP 0 136 453, it is proposed, to remedy this situation, to divide the power emitted by the magnetron into two equal parts and to irradiate each face of the object with it. The distribution of the electromagnetic field inside the object is then symmetrical and can be adjusted as best as possible. We can transmit all the power emitted by the magnetron by a double adaptation, one in front of each side. The adapters neutralize the reflections on the faces and the waves transmitted through the product.

The problem is complicated, however, if heating the object requires the use of two magnetrons at the same time, because the power emitted by one magnetron is too low. If we irradiate each side with a magnetron, the transmitted waves can interfere with the functioning of the other magnetron, sometimes until the destruction of the tubes. The solution which consists in polarizing the incident waves and turning the polarization of the waves relative to each other has often been described. It is well known, but is not always applicable, nor effective, because the transmitted waves have an often multiple polarization because of the diffraction phenomena which take place on the faces of the object.

Similarly, solutions have been recommended where the sources do not emit their power continuously over time, but alternately according to a pulsed regime, so that the wave emitted by one of the magnetrons and received by the other arrives during moments when the latter is off. This decoupling is effective, but also has limits.

The following invention makes it possible to decouple, in a complete manner, the waves emitted by each magnetron with a magic tee or other directional coupler.

Thus, to fix the ideas and take the example above, a bun containing a slice of meat or cheese which comes out of the freezer where it was stored at 18 ° C is according to the invention heated in about 30 seconds instead 5 minutes.

It relates to an installation for heating or microwave treatment of a material, supplied by two separate magnetrons. The magnetrons are mounted on the conjugate branches of a magic tee or a directional coupler; the other conjugate branches, forming a ring, irradiate the material and impedance adapters are located in the lateral branches and / or in front of the magnetrons to decouple the functioning of the magnetrons and transmit all the power emitted by the magnetrons to the material or to the 'object.

The invention also relates to a method for controlling an installation two magnetrons using double balanced mixers to separate the electromagnetic distributions generated by the two magnetrons from each of the contributions.

This process is advantageously automated and the balanced double mixers permanently adjust the settings of the adapters to optimize the operating parameters of the magnetrons, according to a servo-control process.

In this way, a uniform and constant distribution can be obtained over the material or the object. If necessary, we can also take advantage of the settings to distribute the field in a modulated or inhomogeneous way, for example a maximum at the heart of the object and a less field on the surface.

The corresponding installation for heating or microwave treatment of a material comprises an applicator or oven powered by two or more magnetrons and several impedance adapters making it possible to cancel the waves reflected by the applicator, which each of the magnetrons receives. One or more balanced double mixers, the references of which are supplied by a magnetron, detect the part of the waves emitted by this one, among all those received, in order to adjust the impedance adapters and transmit all the power emitted by the magnetrons to material.

In yet another aspect, the invention relates to an installation for heating or microwave treatment of a material, comprising an applicator supplied by two or more magnetrons and several adjustment circuits making it possible to modify the distribution of the waves emitted by each of the magnetrons, transmitted to the applicator and reflected by it. One or more balanced double mixers whose reference channels are supplied by a magnetron, detect the contribution of the waves emitted by each of the other magnetrons, among all the waves received, in order to adjust the circuits modifying the distribution of the electromagnetic field applied to the material and transmit all the power emitted by the magnetrons to it.

In the last two cases, the reference channels of the double mixers can be supplied by an auxiliary generator whose frequency is stabilized on the frequency of one of the magnetrons. - by an auxiliary generator whose frequency is offset from that of a magnetron by a fixed value;

- the reference channels of the balanced double mixers are supplied by a magnetron after equalization of the signal level.

In this context and as will be seen in detail below, four balanced double mixers can be used. For even better optimization, the balanced double mixers will be six in total, the two additional double mixers being used for measurements made in the immediate vicinity or directly in the heart of the material or object or product subjected to microwaves.

The invention will be better understood with reference to the accompanying drawings, given only by way of nonlimiting examples. In these drawings:

FIG. 1 is a schematic assembly diagram of an example of an applicator of a heating or microwave treatment installation which, according to the invention, comprises a magic tee (T) and its associated ring,

FIG. 2 is a schematic perspective view (as an observer would see it along the axis materialized by the arrow P) of the magic tee of the applicator sketched in FIG. 1,

FIG. 3 is a detailed view of an impedance adapter with plunging rod for an applicator as in FIG. 1,

FIG. 4 shows the stationary distributions of the electromagnetic fields created by each of the magnetrons, and by the conjugation of the two in the ring,

FIG. 5 is a geometric perspective view of a first embodiment of an installation according to the invention corresponding to the block diagram of FIG. 1,

FIG. 6 corresponds to FIG. 5, where the sensors enabling the operation of the magnetrons are indicated,

- Figure 7 illustrates another spatial arrangement of an installation according to the invention, comprising two additional waveguides, inserted between the branches and the applicator, at the entrance thereof,

- Figure 8 describes another spatial arrangement for an installation according to the invention using four magnetrons (twice two magnetrons).

FIG. 9 describes yet another arrangement implementing a slot-shaped microwave applicator, advantageous for the continuous treatment of materials moving past the slot delivering the microwave energy, and

- Figures 10s (10a to 10d) group together in the form of a schematic sketch the principles of measurements and calculations used in balanced double mixers for adjusting the operation of the ring.

The operation of the assembly can easily be understood using FIGS. 1 and 2. The object or the material to be heated 10 placed inside an applicator or microwave oven 5 is irradiated by the symmetrical conjugate branches ( waveguides) 1 and 2 of a magic tee (T). The other combined branches (waveguides) 3 and 4, orthogonal to the other two as illustrated in FIG. 2, include the microwave or magnetron sources 11 and 12 materialized by a double arrow (=>). The branches 1 and 2 have equal lengths and the mounting is completely symmetrical. The set of waveguides 1, 2 form a waveguide in the form of a ring or guide ring.

The energy emitted by the magnetron 11, coming from the branch 3 does not leave by the branch 4. It is distributed at the level of the T in two waves of the same phase in the branches 1 and 2. These waves are each reflected on the faces 13 and 14 of the material 10. They remain in phase and combine in the tee to add up in the branch 3. These reflected waves cancel out in the branch 4 for reasons of symmetry. It therefore suffices to have two impedance adapters 6,7 symmetrically in the branches 1 and 2, in front of the faces of the object 10 to cancel them. If the object does not fully absorb the energy, the transmitted waves are themselves in phase. They add up to the level of the T in branch 3 also. It therefore suffices to have a third adapter 8 in the branch 3 in front of the magnetron 11 to prevent them from reaching and disturbing the operation of the magnetron 11. The magnetron 12, which is located in the branch 4 works in the same way. It emits waves in branches 1 and 2 having opposite phases, which are reflected on the faces 101 and 102 with obviously opposite phases. In the tee they cancel out in branch 3 and add up in branch 4 as before, if symmetrical adapters 6,7 in front of faces 101 and 102 eliminate these reflections. The magnetron 12 receives no energy. As previously also, the transmitted waves which come from the magnetron 12 are in phase opposition with respect to each other. They also cancel out in branch 3 of the tee and combine in branch 4 of the magnetron 12 which emitted them. A fourth impedance adapter 9, placed in front of the magnetron 12, prevents them from reaching it.

The decoupling between the two magnetrons is thus as perfect as possible. No wave emitted by the magnetron 11 reaches the magnetron 12 and vice versa. In addition, it is possible to reduce the reflection of the waves emitted by each magnetron and received by itself by means of impedance adapters which operate separately.

Such impedance adapters 6,7,8,9 are shown in FIG. 3. They are of the plunger type, with screw for example, and have 2 degrees of freedom, in height and penetration in the waveguide according to f1, and longitudinally along f2 (rod 6 and slot 6 'in the example of the adapter placed on the waveguide 1).

The arrangement also has the advantage of providing a homogeneous distribution of the electromagnetic field in the product, as can be seen in FIG. 4, which represents the ordinates and in mV the amplitudes E1 and E2 of the electric fields radiated separately by the magnetrons 11 , respectively 12, and the field associated with the total energy resulting from their conjugation, ie E * = E-ι + E ₂ . In ideal cases, E * is a horizontal line.

The stationary distribution of the electromagnetic field produced by the emission of magnetron 11 is symmetrical between the two impedance adapters 6,7 The field has a maximum at the center of the object 10, for example such as the curve (11) of the Figure 3 represents it. The distribution has more or less pronounced maxima and minima depending on the attenuation of the waves in the product. The distance between two consecutive maxima is equal to the wavelength in the material, divided by 2. The stationary distribution of the electromagnetic field produced by magnetron 12 corresponds to waves of the same amplitude but one of the waves is in phase opposition compared to the previous distribution. It follows that the stationary distribution is shifted by a quarter of the wavelength so that its maxima are located at the places where the minima of the stationary distribution of the field emitted by the magnetron 11 are located.

The total energy E * dissipated in the product being proportional to the sum of the squares of the fields of the separate distributions, we see that the heating is much more homogeneous, if we take into account the two distributions than with each of them. If the relative amplitudes of the two distributions are not as desired, the local energy distribution can be adjusted without departing from the scope of the invention, by slightly disrupting the lateral impedance adapters 6,7, located in branches 1 and 2. It will follow, of course, that the waves reflected on the magnetrons will no longer be zero but as the assembly includes adapters of impedance 8.9 in front of each magnetron, we will be able to catch up with the settings with these , because the waves to be compensated in front of each magnetron are well emitted by each magnetron.

It should be noted that the invention described, which uses a magic tee (T) to decouple the operation of two continuously emitting magnetrons, also applies to magnetrons which would operate alternately with respect to each other. The invention reinforces the decoupling that this solution could provide. Likewise, the invention also combines with the conventional means indicated, which amount to rotating the polarization planes of the waves transmitted and reflected or emitted.

It is not going beyond the scope of the invention if the magnetrons are placed in the branches 1 and 2 of the magic tee by feeding the applicator through the branches 3 and 4. The operation can be described in the same way.

One can also use magic Tees other than the Tee drawn in figure 2, which are different in their shape but which function in an identical way.

Similarly, one can use a 3 db directional coupler called Tee at 90 °, consisting of two guides having a common opening on the small common side. This tee has a plane of symmetry different from the magic tee; the waves coming out through them conjugate branches 1 and 2 are in phase quadrature with respect to each other, regardless of the source in 3 or 4. This difference comes back to the situation described for the classic magic tee provided that you choose branch lengths 1 and 2 different (from λ _g / 4).

Similarly, it is possible to use, without departing from the scope of the invention, a directional coupler, having a coupling coefficient different from 3 db, for example 10 db, with two generators of the same nominal power or of different nominal power. The wave circulation takes place as described. The stationary distributions are obviously modified in amplitude, one could for example take advantage of them to overheat, possibly for a given time, a face of the object.

In general, and knowing that the cost price of industrial magnetrons is growing much faster than the nominal power, the use of two weaker magnetrons is a very economical solution compared to the use of a single magnetron. .

It should be noted here that the invention has nothing in common with devices called combiners or assemblers of several high frequency sources or microwaves. These devices have three or more branches. They are used to connect two or more amplifiers and synchronous sources, that is to say powered by the same preamplifier. With these devices, the combination of waves only takes place because the sources are synchronous.

The invention does not use either, and is thereby distinguished from it, a magic tee with a single generator which supplies a separate applicator in two parts or two applicators operating in an identical manner. This assembly, the separate reflected waves of which vary greatly during the treatment, in an identical manner, uses a magic tee to optimize the absorption in the two applicators, without adjustment, as described for example in FR 2 316 761.

A first spatial arrangement for an installation according to the invention is represented for example in FIG. 5, in which the reference numbers of FIGS. 1 to 3 have been used for the identical members or fulfilling the same function. The microwave applicator 5 or oven containing the product to be treated 10, is designed with a door making it possible to introduce and remove therefrom this product 10. We find the magic tee (T) at the junction of branches 3 and 4, waveguides coming respectively from magnetrons 11 and 12, and emerging in the guide ring consisting of branches or waveguides 1 and 2, which leads to the applicator 5. The waveguides are for example of a standard rectangular type of 86 x 43 mm. The ring can be circular or ovoid, or bent with straight parts.

In this case, the position of the adapters 6,7,8,9 can be adjusted once and for all for optimal distribution and in accordance with the invention of the microwave energy received by the product 10, coming from the magnetrons 11 12.

The assembly described in the invention can also be automated and its use can be justified by this fact alone. Indeed, if the dielectric properties of the treated product vary or if the product has a shape which varies, the adjustments of the adapters of the assembly of FIGS. 1 and 2 can be completely automated, as can be seen with reference to FIG. 6.

This is often the case, for example during heating or cooking, where the treated product can swell or shrivel, the dielectric properties then generally changing, and it is then advantageous to be able to modify accordingly and as a function of time. the settings and thus the powers applied.

To do this, there are sensors in front of each magnetron 11,12 in the form of directional measuring couplers 13, respectively 14, allowing the measurement of the incident power Pi and of the reflected power Pr by each magnetron 11 and 12, and we will use then four balanced double mixers to detect microwave signals. Incidentally, this assembly also includes an antenna or sensor 15 in the immediate vicinity of the product 10 to be treated or plugged into the heart thereof. This will be described in more detail later, that is to say after the presentation of other geometrical arrangements of the installation according to the invention, the corresponding reference numbers indicating identical members or of the same functionality.

In fact, FIG. 7 illustrates another assembly of the installation, in which the oven 5 is parallelepidic instead of pyramidal and where between the latter and the waveguides (branches 1,2) are interposed two guides waves 16, respectively 17, inclined with respect to branches 1 and 2, but orthogonal to each other. These two complementary waveguides 16,17 make it possible to act on the orientation of the electric field vectors, thus to adjust the relative values of the coefficients of reflection and of complex transmission and, if necessary, to perfect the decoupling of the magnetrons.

FIG. 8 represents yet another assembly, this time with four magnetrons 11, 12; 11 ', 12' feeding in pair two magic Tees T, T 'with their four branches 1, 2,3,4 (first guide ring), respectively 1,' 2, '3', 4 '

(second guide ring). The two rings open side by side in a 5 'cylindrical oven.

In a variant not shown, it is possible to add a third guide ring supplied by two other magnetrons and placed in a plane orthogonal to the other two, that is to say in a horizontal plane if one referred to the figure 8.

FIG. 9 schematically represents yet another assembly in which the microwave energy is delivered by a slot 18 in an open applicator structure 5 allowing the product to be processed to pass in front of the slot.

Slotted guides, irradiating a material or object placed in an enclosure, are in the mud of many efficient applicators, although it is difficult to obtain a homogeneous distribution of the electromagnetic field in the vicinity of the slots (see in particular Sébastien Keller, Thesis Doctorate, University of Henri Poincaré (Nancy I), November 6, 1997). By feeding a slotted guide with two magnetrons, the problem is simplified.

In such an arrangement, shown in FIG. 9, an electromagnetic field radiator is produced providing a homogeneous distribution in the length direction and homogeneous in the direction perpendicular to the slot. It allows continuous processing, unlike the arrangements in the previous figures, which relate more to batch-by-batch processing. Note that the slot 18 is not located at mid-height, but rather at a height between 2/3 and 3/4 of the height. Preferably, the radiating slit guide is provided with inclined flaps 19, 20. Let us return now and with more details to the balanced double mixers whose role is to follow and process continuously the variations of the parameters measured by the sensors 13,14, according to the principles illustrated in figure 10.

These balanced double mixers are supplied by a microwave reference signal R on their input. They then detect, in a vectorial manner, all the waves synchronous to the reference signal and only the waves synchronous to the reference. We can then combine the signals Pi11, Pr11, Pi12 and Pr12 to obtain

- either an image of the waves reflected in each branch 3 and 4;

- either an image of the signal of imbalance of the waves reflected by each face of the object;

or an image of the imbalance of the waves transmitted by each magnetron.

Pi11 represents the incident power delivered by the magnetron 11,

Pi12 by the magnetron 12, Pr11 represents the power reflected towards the magnetron 11, Pr12 towards the magnetron 12, etc.

This information, which characterizes the amplitudes and the phases of the waves concerned, makes it possible to act on the settings of the four adapters according to a defined regime, according to the desired treatment. A regime can be clearly applied because we know how the elementary waves circulate in the circuit and how we want them to circulate.

Advantageously, the adapters deliver their output signals to a computer, which can be reduced to a simple portable computer, which sends command orders to the adapters 6,7,8,9 so as to always remain in optimal condition by varying, if necessary, the absolute or relative positions of these.

The procedure can also be completed by measuring the distribution of the electromagnetic field directly in the product by means of one (see above) or several antennas, again using double mixers. balanced whose reference signals are the incident waves emitted by each magnetron. We can isolate the values of the electric field produced by each magnetron.

It is possible to supply the reference channels of the double balanced mixers with signals emitted by a single magnetron 11 without using the directional measurement couplers. Generally, the magnetrons are planted in a rectangular guide in front of a short circuit, the position of which is chosen with care so that the magnetron 11 operates in nominal fashion and emits all its power in the guide in the opposite direction. A loop can be mounted in the bottom of the short-circuit to capture by magnetic influence a wave of amplitude proportional to the emission of magnetron 11. This loop can feed the balanced double mixers.

Automatic control of the settings of an oven as described above in its different versions is complicated because the oven has at least four impedance adapters, i.e. at least eight settings in total, because that each adapter has two degrees of freedom, namely its lateral position and its insertion. It must be taken into account that the furnace is fed by at least two magnetrons, that is to say that the electromagnetic field which reigns in the furnace or in all the branches of the ring, is a variable linear combination of the fields electromagnetic emitted by each magnetron. The sensors must therefore select the part of the electromagnetic field emitted by each magnetron and provide double information in amplitude and in phase.

These conditions cannot be ensured with ordinary detectors, with diodes, which only measure the amplitude of the total electromagnetic field. On the other hand, one can reach the fixed objective by using simple mixers. A mixer is a detector which is supplied by two electrical signals, one is called signal S, the other is called reference R. This input is often designated in the technical literature by the expression "local oscillator". A simple mixer supplies a non-zero voltage, only if the two signals R and S have the same frequency and are synchronous. The voltage is proportional to the amplitude of S and to the cosine of the phase of S with respect to R, ie V = S.cosφ.

With two simple mixers, mounted in parallel and with a suitable phase shifter, we know how to make a balanced double mixer. The balanced double mixer provides two output voltages proportional to S.cos φ and S.sin φ when the balanced double mixer is supplied by synchronous S and reference R signals.

It can thus be seen that if the signal R is a wave of the magnetron 11 (for example), it is possible to apply to the input S of a balanced double mixer a complex signal coming from the two magnetrons. It is obtained that the outputs of the balanced double mixer detect only the part of the synchronous electromagnetic field at the signal R; that is to say to the wave emitted by the magnetron 11. In addition, the balanced double mixer provides the amplitude and the phase of the detected part. The two outputs allow you to adjust as you want an impedance adapter.

Returning to FIG. 10, flow diagram of the settings of the four impedance adapters 6-7-8-9, it is possible to have two directional measuring couplers 13 14 in the conjugate branches 3 and 4 of the tee, between the magnetrons and the adapters impedance 8 and 9.

Each measurement coupler supplies two signals proportional respectively to the incident wave and to the reflected wave which circulate in the branches considered, denoted Pi11, Pr12, Pi11, Pr12.

If a balanced double mixer has the incident wave Pi11 as its reference signal and the Pr12 wave as signal S, its outputs will indicate the amplitude and phase of the synchronous wave with the emission of magnetron 11. These outputs will allow to adjust the adapters 6 and 7 so that they are zero, knowing that the adapters 6 and 7 must be positioned symmetrically so that, as seen previously, the wave emitted by the magnetron 11 which is reflected on the face 13 of the object or material 10, or zero.

The adjustment of the symmetry of the adapters can also be controlled by the outputs S of another balanced double mixer whose reference R would be provided by the signal Pi12 and whose signal path would be supplied by the signal Pr11, by arranging so that these outputs are also zero.

If we supply the reference channel R of a third double mixer balanced by the signal Pi11 and its signal channel S by Pr11, we obtain at its output directly information, in amplitude and in phase, which measures the reflected wave which the magnetron 11 receives, and which has been emitted by itself. It can therefore be obtained that it is zero by adjusting the impedance adapter 8 so that these voltages are zero.

According to the same procedure and in the same spirit, if one supplies the reference channel R of a fourth mixer balanced by the signal Pi12 and its signal channel S by the signal Pr12, one obtains at the output information which makes it possible to adjust the impedance adapter located in front of magnetron 12 so that it does not receive any reflected wave.

In the flow chart of the settings of the four impedance adapters presented above, four balanced double mixers are used, the reference channels R of which are supplied by the signals collected by two directional couplers located in front of the magnetrons. Adjusting the impedance adapters is like trying to make the outputs of these balanced double mixers null.

In other words, the adjustments are made by canceling the output signals of the balanced double mixers obtained by:

a) crossing the incident signal Pi of magnetron 11, ie Pi11, with the reflected signal Pr of magnetron 12, or Pr12,

b) crossing the incident signal Pi of magnetron 12, either Pi12, with the reflected signal Pr of magnetron 11, or Pr11,

c) combining the signals Pi11 with Pr11, and

d) combining the Pi12 signals with Pr12.

Figures 10a to 10d correspond to each of the preceding combinations of letters a) to d). In FIG. 10a and in FIG. 10b, the symmetry adjustments are made by controlling the adapters 6, respectively 7, located on the branches 1, respectively 2 of the ring, upstream from the oven 5; in FIG. 10c, the adapter 8 located on the branch 3 is adjusted and in FIG. 10b, the adapter 9 located on the branch 4.

This organization chart can be modified without leaving the framework of the invention presented. It is first possible to supply the reference channels R of the double balanced mixers with signals taken as close as possible to the magnetrons 11 and 12 by antennas located at the bottom of the short-circuit pistons as mentioned above.

We can also evaluate the distribution of the global electromagnetic field applied to the product and act on the settings of the four impedance adapters to obtain the best result. Consider in fact an antenna 15 acting as a sensor as shown in Figure 6, located in the center of the product; it indicates the total field. To evaluate the component 11 of the electromagnetic field, that is to say the part emitted by the magnetron 11, it suffices to connect this antenna to the signal channel S of a fifth balanced double mixer of which the reference channel R is supplied by Pi11. This time, of course, we will then adjust the four impedance adapters together so that the amplitude of component 11 of the electromagnetic field distribution is maximum.

Similarly, a sixth balanced double mixer whose reference channel R is Pi 12 and whose signal channel S is connected to the antenna 15, provides amplitude and phase information relating to the component 12 (emitted by the magnetron 12 ), of the electromagnetic field which reigns in the center of the product. It must be minimal if the four impedance adapters are correctly adjusted.

The settings, as detailed above, aim to deliver to the material or object placed in the applicator 5 a maximum and homogeneous distribution, as indicated in FIG. 4. By managing the settings differently, one can also, as mentioned above, establish an ad hoc distribution that is not spatially homogeneous.

As indicated above, the invention therefore also relates to a heating installation, which comprises the abovementioned adjustment means, and means for controlling the adapters (6,7,8,9) to adjust them continuously as a function of the signals delivered by balanced double adapters and ensure optimal distribution over the material or object.

Balanced double mixers are commercially available devices. They are for example manufactured by ANAREN or MINI-CIRCUITS in the United States of America. The present invention can be implemented in microwave installations of any type, for household electrical installations for defrosting or cooking food or heating drinks, such as for industrial installations in the food sector or more generally in the processing of materials.

A particularly interesting application is that of waste treatment as described for example in WO 97/44069, in particular infectious waste, in order to be able to landfill or recycle it rather than incinerate it, an operation which is always extremely expensive. Such an installation could constitute the centerpiece.

Claims

1. Installation for heating or microwave treatment of a material or object comprising an applicator or oven (5) supplied by two separate magnetrons (11,12), characterized in that the magnetrons are mounted on the branches (3, 4) combined with a magic tee or a directional coupler, forming a ring, that the other branches (1,2) conjugate irradiate the material (10) and that we have impedance adapters (8,9) in the branches (3,4) and / or in front of the magnetrons (11, 12) to decouple the functioning of the magnetrons and transmit all the power emitted by the magnetrons to the material or to the object.

2. Heating installation according to claim 1, characterized in that impedance adapters (6,7) make it possible to cancel the waves reflected by the applicator (5) that each of the magnetrons receives, and in that it includes one or more balanced double mixers, the references of which are supplied by a magnetron, to detect the share of the waves emitted by this one, among all those received, in order to adjust the impedance adapters (6,7).

3. Heating installation according to claim 2, characterized in that it comprises several adjustment circuits making it possible to modify the distribution of the waves emitted by each of the magnetrons, transmitted to the applicator (5) and reflected by the latter, the reference channels of the balanced double mixers being supplied by a magnetron to detect the contribution of the waves emitted by each of the other magnetrons among all the waves received, in order to adjust the circuits modifying the distribution of the electromagnetic field applied to the object or to the material.

4. Heating installation according to claim according to 2 or 3, characterized in that the reference channels of the double mixers are supplied by an auxiliary generator whose frequency is stabilized on the frequency of one of the magnetrons

- by an auxiliary generator whose frequency is offset from that of a magnetron by a fixed value;

- the reference channels of the double mixers are powered by a magnetron after equalization of the signal level.

5. Method for controlling an installation with two separate magnetrons, characterized in that the electromagnetic distributions generated by the two magnetrons are separated from the contributions coming from each of them using double balanced mixers.

6. Method according to claim 5, characterized in that with the aid of balanced mixers, the settings of the adapters are continuously adjusted to optimize the operating parameters of the magnetrons.

7. Method according to claim 6, characterized in that the adjustments are made so as to obtain a constant, homogeneous and maximum distribution on the material or the object.

8. Method according to claim 7, characterized in that the adjustments consist in canceling the output signals of the balanced double mixers obtained by:

a) crossing the incident signal Pi of the magnetron (11), either (Pi11,) with the reflected signal Pr of the magnetron (12), or (Pr12),

b) - crossing the incident signal Pi of the magnetron (12), either (Pi12), with the reflected signal Pr of the magnetron (11), or (Pr11),

c) combining the signals (Pi11) with (Pr11), and

d) combining the signals (Pi12) with (Pr12).

9. Method according to claim 6, characterized in that the adjustments are made so as to obtain a modulated distribution on the material or the object, in particular maximum in the center and least in surface.

10. Automated heating installation according to one of claims 1 to 4, characterized in that it comprises means for adjusting the method according to one of claims 5 to 9, and means for controlling the adapters (6,7 , 8,9) to adjust them continuously according to the signals delivered by the balanced double adapters and to ensure an optimal distribution on the material or the object.

1. Use of the installation according to any one of claims 1 to 5 or 1 in the treatment of infectious waste, in particular hospital waste.